The present invention generally relates to plasma treating methods, and more particularly to a plasma treating method which uses a hydrogen gas.
Various proposals have been made to carry out a plasma treating of a solid surface using a gas which includes hydrogen. For example, Fujimura et al., Procedures of The Symposium on Dry Process, Edited by Nishizawa et al., PV 88-7, The Electromechanical Society, Inc. 1988, pp. 126-133 proposes a method of removing a resist layer which is used as a mask during an ion implantation. On the other hand, K. Miyake, "Removal of a Thin SiO.sub.2 Layer by Low-Energy Hydrogen Ion Bombardment at Elevated Temperatures", Japanese Journal of Applied Physics, Vol. 28, No. 11, November, 1989, pp. 2376-2381 proposes a method of cleaning a silicon surface using hydrogen ions drawn out from the plasma. The present invention relates to a plasma treating method which uses a hydrogen gas and is applicable to the proposed methods described above.
For example, when using hydrogen in a pre-process which is carried out before epitaxially growing a layer on a silicon substrate, this pre-process is generally carried out by heating the substrate to a high temperature within a hydrogen atmosphere. Because the process uses a large quantity of hydrogen, the hydrogen is, for safety reasons, usually diluted by a gas such as nitrogen gas and argon gas which do not react with hydrogen. The pre-process using the hydrogen is carried out mainly for the purpose of removing a natural oxide layer which is formed on the silicon substrate, for example. Safety precautions must be taken during this pre-process, because the substrate temperature is raised to a high temperature on the order of 1000.degree. C. and the hydrogen gas is supplied at a rate of 10 to 1000 liters/minute.
Hence, M. Miyake referred above proposes the plasma treating which can be carried out at a relatively low temperature, with an improved safety and high efficiency. In addition, Fujimura et al. referred above proposes the use of hydrogen plasma to remove ion implanted resist.
According to the conventional plasma treating methods which use hydrogen, the hydrogen gas itself is used, or a hydrogen gas which is diluted by an inert gas or nitrogen gas is used. However, there is a problem in that the ashing rate is poor and the process takes too long a time for practical purposes.
The main object of the plasma treating is to utilize hydrogen ions (H.sup.+) and hydrogen radicals (hydrogen atoms H). For this reason, it is possible to employ an electron cycrotron resonance (ECR) plasma in order to improve the dissociation of the hydrogen and increase the speed of the process. However, it still takes a relatively long time to carry out the process and the use of the ECR plasma is still unsatisfactory for practical purposes.